The present invention relates to alloys including fine metal oxide particles, and in particular to a method of manufacturing such alloys by utilization of an oxidization reduction reaction.
In the prior art, alloys in which a metal oxide is finely dispersed in a base metal have conventionally been made by, for example, (1) the so called powder metallurgy method, in which a powder of the metal oxide and a powder of the base metal are mixed together and then the mixture of these powders is heated to a high temperature and is sintered; (2) the method in which a powder of the metal oxide is formed into a porous solid and then the molten base metal is caused to permeate this porous solid, possibly under pressure; and (3) the so called internal oxidization method, in which a metal solid is formed of the base metal and of the metal of which it is desired to utilize the oxide, and then oxygen is supplied from the surface of the metal solid to the interior of the solid, so that the metal of which it is desired to utilize the oxide is oxidized (this metal should have a higher tendency to become oxidized than the base metal).
The methods (1) and (2) above allow an alloy in which the metal oxide is finely dispersed to be made relatively cheaply and efficiently, but the following problems arise. First, the combination of base metal and metal oxide is restricted to a combination in which there is mutual chemical stability, so that the manufacture of an alloy of arbitrary chemical composition is difficult. Also, there is a tendency for the surface tension between the base metal and the metal oxide to be insufficient, and this gives rise to problems with the strength of the resulting alloy. Further, a tendency arises, when a part made of the alloy is in sliding frictional contact with another element such as a mating member, that particles of the metal oxide should become detached from said part made of the alloy, thus causing undue wear and also causing damage, such as scuffing, to the mating member. In particular, in the case of the sintering method (1), since it is difficult to avoid completely that some of the air or atmospheric gas present among the powders from beforehand should remain after the sintering process, the manufacture of an alloy with a full 100% density is difficult, and further the problems exist of heating to a high temperature in the sintering stage and of control of the atmosphere. Further, in the case of method (3) above, i.e. the so called internal oxidation method, a alloy in which the surface tension between the base metal and the metal oxide particles included therein can be manufactured which has excellent characteristics, but there arise the problems that since the solid metal must be heated to a high temperature near to its melting point for a long time the manufacturing cost is high, and further that when the volume of the alloy to be manufactured is required to be great it is difficult to ensure that the metal oxide is dispersed satisfactorily within the resulting compound material as far as its center; in other words, it is difficult to control the size and dispersion pattern of the included particle mass metal oxide.
In Japanese Patent Application Ser. No. 58-13810 (1983), the applicant of which was the same as the applicant of the Japanese application of which priority is being claimed in the present patent application and as the assignee of the present patent application, and which it is not hereby intended to admit as prior art except to the extent otherwise obliged by law, there has been proposed a method of manufacture of an alloy of a first metal and a second metal whose melting point is lower than the melting point of said first metal, characterized in that: a porous body is formed from the first metal; the porous body is disposed within a mold; the second metal in molten form is poured into the mold; the first metal and the second metal are alloyed together by causing the molten metal to permeate the porous body (as by the application of pressure); and thus an alloy is formed such that in the region where the porous body originally was the second metal does not substantially exist by itself any more. According to this method, it is certainly possible to manufacture an alloy of a type which cannot be made by conventional methods; but this method is not suitable for manufacturing an alloy in which particles of a metal oxide are finely dispersed.